During the patients' participation, 6 visits are planned: an inclusion visit then, a follow-up visit at 1, 2 and 3 months from the inclusion visit, and a final evaluation visit at 4 months from the inclusion visit. At each visit, synovitis will be evaluated using both methods: clinical examination and ultrasonography. For a same patient, clinical evaluation of synovitis will have to be performed - during the entire study - by the same rheumatologist and the ultrasonographic evaluation will have to be performed by the same ultrasonographist (different from the rheumatologist) and always using the same ultrasonograph.